This invention relates to an improved hot wire arc welding torch, and to a conduit cable therefor.
U.S. Pat. Nos. 3,122,629 and 3,163,743 disclose an arc welding method which does not consume any electrode, but employs a hot wire. According to this method an electric current is supplied to a wire so that it may be heated by the Joule effect, (I.sup.2 R) and fed to an arc. This method enables welding at a greatly improved rate as compared with welding in which the wire is not heated, but is not well suited for manual usage since it requires two relatively large torches, i.e., a torch for producing an arc and a torch for heating the wire. In order to enable manual welding it is necessary to construct the two torches as an integral assembly, and to reduce its size as far as practically possible. To reduce the size of the assembly it is beneficial to secure the wire heating torch closely adjacent to the TIG (Tungsten Inert Gas) torch with the wire feed end of the former inclined relative to the TIG torch.
A known apparatus of this type is shown in FIG. 1, wherein a TIG torch 1 holds a coaxial tungsten electrode 2. A shielding nozzle 3 shields an arc 6 and a weld puddle 10 with inert gas. A holder 4 secures a wire heating torch to the TIG torch. The holder 4 is a split clamping ring having a slot 8 which is narrowed to secure the wire heating torch to the TIG torch by tightening a bolt 7. A vertical adjusting unit 11 includes a threaded guide bar 15 along which a horizontal adjusting unit 12 is moved by turning a knob 13. The horizontal adjusting unit includes parallel guide bars 16 along which a cylindrical housing fixture 24 is movable by rotating a knob 14.
A supply conduit 17 is secured in the center of a current feeder 19. A copper wire 18 has one end brazed to the current feeder, while the other end of the wire is connected to an alternating current power source 20 for heating the wire. The current feeder 19 has an internally threaded lower end which receives a current feeding tip 22. An insulating cap nut 21 is disposed between the current feeder 19 and the tip 22. An insulating spacer 23 has an enlarged diameter flange at its upper end, and isolates the tip 22 from the fixture 24. A guide member 26 is threaded into the lower end of the fixture 24, and mounts an insulating sleeve 25 which guides a feed wire 5. An insulating cap tube 34 surrounds the current feeder 19.
In operation, the lower ends of the electrode 2 and the wire 5 are appropriately positioned relative to each other by the vertical and horizontal adjusting units 11 and 12 on which the housing fixture 24 is mounted. The wire 5 supplied from a source (not shown) to the conduit 17 is fed into the weld puddle 10 through the tip 22, the insulating spacer 23 and the insulating guide sleeve 25. An electric current for heating the wire 5 is supplied from the power source 20 to the tip 22 through the copper wire 18 and the current feeder 19. The wire 5 is heated to a temperature just below its melting point due to the resistance of the wire between the lower end of the tip 22 and the weld puddle 10. The working end of the wire is thereafter melted by the heat of the arc 6 and the weld puddle, and the molten wire material is thus fused to the workpiece 9.
This prior art type of hot wire arc welding torch construction has a relatively wide wire feed angle .crclbar., which makes it rather large, cumbersome and difficult to handle and manipulate. Moreover, as the insulating spacer 23 has a smooth outer peripheral surface, the exchange or replacement of the current feeding tip 22 is likely to result in the simultaneous detachment of the insulating spacer and its breakage by falling onto the floor.
A further aspect of this invention relates to a conduit cable for a hot wire type of arc welding torch. A typical prior art construction of such a conduit cable arrangement is shown in FIGS. 4 through 6, wherein a TIG torch 1 is coupled to a wire heating torch 42, and a cable 43 for the TIG torch comprises a gas hose 46, a water hose 47, a power cable 48 and a control cable 49. A conduit cable 44 is connected to a wire supply source (not shown), and feeds the welding wire 5 to the welding zone after it has been electrically heated by the torch 42.
FIG. 5 shows the end of the cable 44 which is connected to the wire supply source. A fixture 80 is secured to a connector 70 in the wire supply source, and has an axial bore in which a liner 60 is disposed for guiding the welding wire. The liner 60 is protected by a spring tube 50 which comprises a tight coil of steel wire. An insulating tube 51 surrounds the spring tube to prevent any electrical shock in the event that the liner 60 becomes worn to bring the welding wire into contact with the spring tube. A reinforcing rubber sleeve 90 protects the cable 44 against distortion when it is connected to the wire supply source.
FIG. 6 shows the end of the cable 44 which is connected to the wire heating torch 42. A tip 56 for feeding electrical current to the welding wire is threaded to a fixture 54, and secured to the wire heating torch 42 by a thumb screw 55. A power cable 45 for supplying electrical current to the torch is provided at its opposite ends with terminals 52 and 58 which are secured to the connector 70 and the torch 42 by bolts 53 and 57.
The current feeding tip 56 and the liner 60 are consumable parts which become worn as the welding wire passes through them, whereby they must be periodically changed. To install a new tip the thumb screw 55 is loosened and the bolt 57 securing the power cable 45 is removed so that the cable and the tip may be detached from the torch 42 together. The tip is thereafter unscrewed from the fixture 54, and a new tip is installed. If it is necessary to change the liner 60, the fixture 80 for the cable 44 and the power cable 45 are detached from the connector 70, whereafter the liner is removed and exchanged for a new one.
In such a conventional conduit cable construction it is necessary to detach the electrical power cable when changing consumable parts such as the current feeding tip and the liner, which is both troublesome and time consuming. Moreover, the thumb screw securing the tip to the wire heating torch can easily become loosened during use. Finally, as the liner is only reinforced by the spring tube, fine "stuttering" vibrations are often generated due to the resistance of the wire as it is being fed, and such feed rate disruptions can adversely affect the quality of the weld bead.